Role of Intestinal Microbiota in Ulcerative Colitis

Theoretical part
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2. The colonic environment
As for Bacteroides, it has been shown that many of these genes are located in clusters (Schell et
al., 2002;Ventura et al., 2007;Tasse et al., 2010;Pokusaeva et al., 2011). Genome sequencing of
the different Bifidobacterium species has revealed that carbohydrate modifying enzymes can vary
among species. Additionally, the affinity of the enzymes may vary depending on the length and
complexity of the substrate (Warchol et al., 2002;Margolles and de los Reyes‐Gavilan, 2003;Janer
et al., 2004). Table 1 lists some of the GH found in Bifidobacterium spp.
Most of the biochemical characterized GH from Bifidobacterium spp. have shown to be active
towards oligosaccharides, but only some GH are active towards polysaccharides (Van Den Broek
and Voragen, 2008). Van Laere and colleagues (2000) studied the ability of four Bifidobacterium
species (B. breve, B. longum, B. infantis and B. adolescentis) to ferment plant polysaccharides and
their corresponding oligosaccharides in vitro. The results showed that the ability to ferment plant
cell wall derived polysaccharides varied depending on Bifidobacterium species, but most of the
species were able to ferment oligosaccharides. B. breve could ferment arabinogalactan, but not
arabinan and arabinoxylan. This was in line with results from genome sequencing that has
revealed the absence of arabinan‐ and arabinoxylan degrading enzymes in B. breve (Table 1). B.
infantis was not able to ferment any of the polysaccharides even though genome sequencing has
revealed that it may contain α‐L‐arabinofuranosidase (Table 1). Additionally, B. infantis was only
able to utilize arabino‐galactooligosaccharides. These results could indicate that the α‐L‐
arabinofuranosidase found in B. infantis has a low affinity for plant polysaccharides but specificity
for certain oligosaccharides. B. longum was able to utilize arabinogalactan, arabinan, and
arabinoxylan. This is in agreement with previous work by Gueimonde et al. (2007), which showed
that α‐L‐arabinofuranosidase activity in B. longum could be induced by arabinose‐ and/or xylose‐
containing polymers and/or their related oligosaccharides. Genome sequencing of B. longum has
revealed that more than 8% of the genome is related to the catabolism of oligo‐ and
polysaccharides. Among these genes, many were predicted to encode proteins involved in
catalyzing the degradation of arabinose‐containing saccharides such as intra‐ and extracellular α‐L‐
arabinofuranosidases (Schell et al., 2002). This provides B. longum with a competitive advantage in
the utilization of different substrates in the gut (Van Den Broek and Voragen, 2008).